Project Summary/Abstract: Deafness and balance disorders resulting from the loss of sensory hair cells of the inner ear are a major cause of disability and morbidity in the US. In mammals, the cells of the various sensory epithelia of the inner ear arise embryonically and subsequently do not regenerate if damaged (Rubel et al., 2013). Hearing loss resulting from the death of hair cells in the organ of Corti is thus permanent, and treatments aimed at reversing hearing loss through stimulated regeneration of hair cells are badly needed. However, experimentation on the cells of the inner ear is difficult due to their small number and extreme inaccessibility in the adult. As a result, modern techniques of cell and molecular analysis and drug discovery have been difficult to apply, and aside from prosthetics, treatment options for sensorineural deafness remain few. To overcome these problems, and in pursuit of new treatments for hair cell loss, we have used powerful new ?direct lineage reprogramming? technologies, originally developed for neuron-specific reprogramming (Son et al., 2011; Vierbuchen et al., 2010), to generate hair cell-like cells in vitro, directly from mouse and human somatic cells (fibroblasts and inner ear supporting cells). This advance allows a new range of experimentation into the mechanisms of hair cell differentiation, the development of preclinical models of genetic hearing loss (disease modeling), high-throughput screening for drug discovery related to regeneration and ototoxicity, and the application of gene therapy approaches to the problem of hair cell regeneration. The Aims of the proposal include: 1) Development of improved reprogramming strategies to induce mouse and human hair cell-like cells. 2) Development of a drug screen for ototoxicity, and an in vitro disease model of genetic hearing loss. 3) A test of reprogramming in a preclinical model of hair cell regeneration/replacement in long-deafened mice.